Variable Interest Entities - Assets and Liabilities of Consolidated VIEs (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents		$ 663	$ 587	$ 1,349	$ 898
Restricted cash		438	358	247	207
Accounts Receivable, net
Customer		3,231	4,592
Unamortized energy contract assets, current		38	47
Mark-to-market derivative assets, current		644	679
Inventories, net
Materials and supplies		1,425	1,456
Assets held for sale		958	0
Other current assets		1,609	905
Total current assets		12,562	12,037
Property, plant and equipment, net		82,584	80,233
Nuclear decommissioning trust funds		14,464	13,190
Unamortized energy contract assets, noncurrent		294	336
Other Assets, Noncurrent		2,982	3,197
Total assets	[1]	129,317	124,977
Current liabilities
Long-term debt due within one year		1,819	4,710
Accounts payable		3,562	3,560
Accrued expenses		2,078	1,981
Market-to-market derivative liabilities, current		295	247
Unamortized energy contract liabilities		100	132
Liabilities held for sale		375	0
Other current liabilities		1,264	1,331
Total current liabilities		12,771	14,185
Long-term debt		35,093	31,329
Asset retirement obligations		12,300	10,846
Liability, Defined Benefit Pension Plan, Noncurrent		4,503	4,247
Unamortized energy contract liabilities		238	338
Other deferred credits and other liabilities		2,942	3,064
Total liabilities	[1]	94,449	90,404
Exelon Generation Co L L C [Member]
Current assets
Cash and cash equivalents		226	303	750	416
Restricted cash		89	146	153	138
Accounts Receivable, net
Customer		1,298	2,893
Unamortized energy contract assets, current		38	47
Mark-to-market derivative assets, current		644	675
Inventories, net
Materials and supplies		978	1,026
Assets held for sale		958	0
Other current assets		1,357	605
Total current assets		6,947	7,076
Property, plant and equipment, net		22,214	24,193
Nuclear decommissioning trust funds		14,464	13,190
Unamortized energy contract assets, noncurrent		293	336
Other Assets, Noncurrent		1,826	1,960
Total assets	[2]	48,094	48,995
Current liabilities
Long-term debt due within one year		197	2,624
Accounts payable		1,253	1,692
Accrued expenses		788	786
Market-to-market derivative liabilities, current		262	215
Unamortized energy contract liabilities		7	17
Liabilities held for sale		375	0
Other current liabilities		444	517
Total current liabilities		5,219	7,289
Long-term debt		5,566	4,464
Asset retirement obligations		12,054	10,603
Unamortized energy contract liabilities		3	11
Other deferred credits and other liabilities		1,308	1,415
Total liabilities	[2]	33,418	33,165
Pepco Holdings LLC [Member]
Current assets
Cash and cash equivalents		111	131	124	30
Restricted cash		39	36	43	42
Accounts Receivable, net
Customer		525	479
Inventories, net
Materials and supplies		198	190
Other current assets		45	49
Total current assets		1,599	1,480
Property, plant and equipment, net		15,377	14,296
Other Assets, Noncurrent		307	323
Total assets		23,736	22,719
Current liabilities
Long-term debt due within one year		347	103
Accounts payable		539	462
Accrued expenses		299	296
Unamortized energy contract liabilities		92	115
Other current liabilities		141	131
Total current liabilities		2,154	1,612
Long-term debt		6,659	6,460
Asset retirement obligations		59	57
Unamortized energy contract liabilities		235	327
Other deferred credits and other liabilities		622	577
Total liabilities	[3]	13,692	13,111
Atlantic City Electric Company [Member]
Current assets
Cash and cash equivalents		17	12	7	2
Restricted cash		3	2	$ 4	$ 6
Accounts Receivable, net
Customer		124	108
Inventories, net
Other current assets		3	5
Total current assets		326	270
Property, plant and equipment, net		3,475	3,190
Other Assets, Noncurrent		50	53
Total assets	[4]	4,286	3,933
Current liabilities
Long-term debt due within one year		261	20
Accounts payable		177	144
Accrued expenses		46	42
Other current liabilities		11	9
Total current liabilities		780	360
Long-term debt		1,152	1,307
Other deferred credits and other liabilities		48	39
Total liabilities	[4]	2,895	2,657
Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents		98	163
Restricted cash		47	88
Accounts Receivable, net
Customer		148	151
Other		36	39
Unamortized energy contract assets, current		22	23
Inventories, net
Materials and supplies		244	227
Assets held for sale		101	0
Other current assets		674	32
Total current assets		1,370	723
Property, plant and equipment, net		5,803	6,022
Nuclear decommissioning trust funds		3,007	2,741
Unamortized energy contract assets, noncurrent		249	250
Other Assets, Noncurrent		52	89
Total noncurrent assets		9,111	9,102
Total assets		10,481	9,825
Current liabilities
Long-term debt due within one year		94	544
Accounts payable		81	106
Accrued expenses		70	70
Unamortized energy contract liabilities		4	8
Liabilities held for sale		16	0
Other current liabilities		5	3
Total current liabilities		270	731
Long-term debt		889	527
Asset retirement obligations		2,318	2,128
Unamortized energy contract liabilities		0	1
Other deferred credits and other liabilities		129	89
Total noncurrent liabilities		3,336	2,745
Total liabilities		3,606	3,476
PP&E - unrestricted asset		1	20
AHFS - unrestricted asset		9	0
Variable Interest Entity, Primary Beneficiary [Member] | Recourse [Member]
Current liabilities
Total liabilities		8	3
Variable Interest Entity, Primary Beneficiary [Member] | Exelon Generation Co L L C [Member]
Current assets
Cash and cash equivalents		98	163
Restricted cash		44	85
Accounts Receivable, net
Customer		148	151
Other		36	39
Unamortized energy contract assets, current		22	23
Inventories, net
Materials and supplies		244	227
Assets held for sale		101	0
Other current assets		669	31
Total current assets		1,362	719
Property, plant and equipment, net		5,803	6,022
Nuclear decommissioning trust funds		3,007	2,741
Unamortized energy contract assets, noncurrent		249	250
Other Assets, Noncurrent		42	73
Total noncurrent assets		9,101	9,086
Total assets		10,463	9,805
Current liabilities
Long-term debt due within one year		68	523
Accounts payable		81	106
Accrued expenses		70	70
Unamortized energy contract liabilities		4	8
Liabilities held for sale		16	0
Other current liabilities		5	3
Total current liabilities		244	710
Long-term debt		889	504
Asset retirement obligations		2,318	2,128
Unamortized energy contract liabilities		0	1
Other deferred credits and other liabilities		129	89
Total noncurrent liabilities		3,336	2,722
Total liabilities		3,580	3,432
PP&E - unrestricted asset		1	20
AHFS - unrestricted asset		9	0
Variable Interest Entity, Primary Beneficiary [Member] | Exelon Generation Co L L C [Member] | Recourse [Member]
Current liabilities
Total liabilities		8	3
Variable Interest Entity, Primary Beneficiary [Member] | Pepco Holdings LLC [Member]
Current assets
Cash and cash equivalents		0	0
Restricted cash		3	3
Accounts Receivable, net
Customer		0	0
Other		0	0
Unamortized energy contract assets, current		0	0
Inventories, net
Materials and supplies		0	0
Assets held for sale		0	0
Other current assets		5	1
Total current assets		8	4
Property, plant and equipment, net		0	0
Nuclear decommissioning trust funds		0	0
Unamortized energy contract assets, noncurrent		0	0
Other Assets, Noncurrent		10	16
Total noncurrent assets		10	16
Total assets		18	20
Current liabilities
Long-term debt due within one year		26	21
Accounts payable		0	0
Accrued expenses		0	0
Unamortized energy contract liabilities		0	0
Liabilities held for sale		0	0
Other current liabilities		0	0
Total current liabilities		26	21
Long-term debt		0	23
Asset retirement obligations		0	0
Unamortized energy contract liabilities		0	0
Other deferred credits and other liabilities		0	0
Total noncurrent liabilities		0	23
Total liabilities		26	44
Variable Interest Entity, Primary Beneficiary [Member] | Atlantic City Electric Company [Member]
Current assets
Cash and cash equivalents		0	0
Restricted cash		3	3
Accounts Receivable, net
Customer		0	0
Other		0	0
Unamortized energy contract assets, current		0	0
Inventories, net
Materials and supplies		0	0
Assets held for sale		0	0
Other current assets		0	0
Total current assets		3	3
Property, plant and equipment, net		0	0
Nuclear decommissioning trust funds		0	0
Unamortized energy contract assets, noncurrent		0	0
Other Assets, Noncurrent		10	14
Total noncurrent assets		10	14
Total assets		13	17
Current liabilities
Long-term debt due within one year		21	20
Accounts payable		0	0
Accrued expenses		0	0
Unamortized energy contract liabilities		0	0
Liabilities held for sale		0	0
Other current liabilities		0	0
Total current liabilities		21	20
Long-term debt		0	21
Asset retirement obligations		0	0
Unamortized energy contract liabilities		0	0
Other deferred credits and other liabilities		0	0
Total noncurrent liabilities		0	21
Total liabilities		$ 21	$ 41

[1] Exelon’s consolidated assets include $10,200 million and $9,532 million at December 31, 2020 and 2019, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,598 million and $3,473 million at December 31, 2020 and 2019, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 23–Variable Interest Entities for additional information.

[2] Generation’s consolidated assets include $10,182 million and $9,512 million at December 31, 2020 and 2019, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,572 million and $3,429 million at December 31, 2020 and 2019, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 23–Variable Interest Entities for additional information.

[3] PHI’s consolidated total assets include $18 million and $20 million at December 31, 2020 and 2019, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $26 million and $44 million at December 31, 2020 and 2019, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 23 - Variable Interest Entities for additional information.

[4] ACE’s consolidated assets include $13 million and $17 million at December 31, 2020 and 2019, respectively, of ACE’s consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated liabilities include $21 million and $41 million at December 31, 2020 and 2019, respectively, of ACE’s consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 23 - Variable Interest Entities for additional information.